Foamable polyamide composition and foam obtained therefrom

ABSTRACT

Provided is a foamable polyamide composition comprising a) at least one polyamide comprising at least one carboxylic group; b) at least one thermoplastic rubber; and c) at least one compound having at least one isocyanate group; and optionally d) at least one filler and e) at least one additive.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation application, filed pursuant to35 U.S.C. § 120, of U.S. patent application Ser. No. 15/033,380, filedon Apr. 29, 2016, which is a U.S. national phase entry under § 371 ofInternational Application No. PCT/EP2014/072194, filed on Oct. 16, 2014,which, in turn, claims priority to European Application No. 13190717.2,filed on Oct. 29, 2013. The entire contents of these applications areincorporated herein by reference for all purposes.

FIELD OF THE INVENTION

The present invention relates to foamable polyamide compositions, toprocesses for producing the same, and to a foam comprising the same. Thefoam comprising the polyamide composition according to the presentinvention can be advantageously used as a light-weight material in amotor vehicle application.

BACKGROUND OF THE INVENTION

A polyamide is one of the polymers which are frequently used asengineering plastics for a very wide range of applications.

A foamable polyamide composition is of significant commercial interestand may be used as a light-weight material in aeronautical or motorvehicle, packaging or sound insulation applications, etc.

The foamable polyamide composition may be prepared by chemical methods.For instance, U.S. patent application publication No. 2006/0167124discloses an expandable polyamide composition comprising at least oneisocyanate function, a polyamide and a compound comprising at least onecarboxylic acid function, and polyamide foams obtained therefrom.

For particular applications, such as a motor vehicle application,required is a foamable polyamide composition which is capable ofproviding polyamide foams having a higher foaming ratio than theconventional polyamide foams while still exhibiting excellent mechanicalproperties. Often, an addition of higher amount of isocyanate compoundto polyamide matrix can result in a higher foaming ratio in thepolyamide foam, yet such use of higher amount of isocyanate compound maydegrade the mechanical properties of the polyamide foam, such asflexural strength, flexural modulus and impact strength, which arenecessarily required in certain applications.

Therefore, the foamable polyamide composition which can attain a highdegree of foaming with a less addition of isocyanate compound isrequired in this technology field.

DESCRIPTION OF THE INVENTION

The object of the present invention is therefore to provide a foamablecomposition, which enables obtaining a foam having a high foaming ratiowhile maintaining other advantageous mechanical parameters, such asflexural strength, flexural modulus and impact strength, even with alimited use of isocyanate compound.

The present invention relates to a composition comprising:

-   a) 21.0 to 99.6 wt % of at least one polyamide comprising at least    one carboxylic group;-   b) 0.3 to 9.0 wt % of at least one thermoplastic rubber;-   c) 0.1 to 3.0 wt % of at least one compound having at least one    isocyanate group;-   d) 0 to 65.0 wt % of at least one filler; and-   e) 0 to 2.0 wt % of at least one additive,    wherein the sum of wt % of a) to e) adds to 100 wt %.

Indeed, it has been surprisingly found by the present inventors that asuperior foaming ratio can be obtained by the composition according tothe present invention, even with a limited amount of a compound havingat least one isocyanate group, which is to be added to a polyamidematrix.

One of the essential features of the present invention resides in anaddition of a thermoplastic rubber along with a compound having at leastone isocyanate group to polyamide matrix. It has also been unexpectedlyfound that both excellent foaming ratio as well as satisfactorymechanical properties can be attained through combined use of the twocomponents in the foamable polyamide composition.

In the present invention, the term “polyamide” is intended to denote inparticular a polyamide comprising recurring units complying with any offormula (I) or formula (II) [recurring units (R_(PA))]:—NH—R¹—CO—  formula (I):—NH—R²—NH—CO—R³—CO—,  formula (II):wherein:

-   -   R¹, equal to or different from each other at each occurrence, is        a divalent hydrocarbon group having from 1 to 17 carbon atoms;    -   R², equal to or different from each other at each occurrence, is        a divalent hydrocarbon group having from 1 to 18 carbon atoms;        and    -   R³, equal to or different from each other at each occurrence, is        a divalent hydrocarbon group having from 1 to 16 carbon atoms.

The polyamide of the inventive composition is preferably an aliphaticpolyamide, that is to say that R¹, R² and R³ are aliphatic groups.

Recurring units (R_(PA)) of the polyamide can be notably obtainedthrough polycondensation reaction of (1) one of β-lactam,5-amino-pentanoic acid, ε-caprolactam, 9-aminononanoic acid,10-aminodecanoic acid, 11-aminoundecanoic acid, 12-aminododecanoic acidand/or (2) polycondensation reaction of at least one of oxalic acid(HOOC—COOH), malonic acid (HOOC—CH₂—COOH), succinic acid[HOOC—(CH₂)₂—COOH], glutaric acid [HOOC—(CH₂)₃—COOH], adipic acid[HOOC—(CH₂)₄—COOH], 2,4,4-trimethyl-adipic acid[HOOC—CH(CH₃)—CH₂—C(CH₃)₂—CH₂—COOH], pimelic acid [HOOC—(CH₂)₅—COOH],suberic acid [HOOC—(CH₂)₆—COOH], azelaic acid [HOOC—(CH₂)₇—COOH],sebacic acid [HOOC—(CH₂)₈—COOH], undecanedioic acid [HOOC—(CH₂)₉—COOH],dodecandioic acid [HOOC—(CH₂)₁₀—COOH], tetradecandioic acid[HOOC—(CH₂)₁₂—COOH], octadecandioic acid [HOOC—(CH₂)₁₆—COOH] with atleast one of diamines, such as 1,4-diamino-1,1-dimethylbutane,1,4-diamino-1-ethylbutane, 1,4-diamino-1,2-dimethylbutane,1,4-diamino-1,3-dimethylbutane, 1,4-diamino-1,4-dimethylbutane,1,4-diamino-2,3-dimethylbutane, 1,2-diamino-1-butylethane,1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diamino-octane,1,6-diamino-2,5-dimethylhexane, 1,6-diamino-2,4-dimethylhexane,1,6-diamino-3,3-dimethylhexane, 1,6-diamino-2,2-dimethylhexane,1,9-diaminononane, 1,6-diamino-2,2,4-trimethylhexane,1,6-diamino-2,4,4-trimethylhexane, 1,7-diamino-2,3-dimethylheptane,1,7-diamino-2,4-dimethylheptane, 1,7-diamino-2,5-dimethylheptane,1,7-diamino-2,2-dimethylheptane, 1,10-diaminodecane,1.8-diamino-1,3-dimethyloctane, 1,8-diamino-1,4-dimethyloctane,1.8-diamino-2,4-dimethyloctane, 1,8-diamino-3,4-dimethyloctane,1.8-diamino-4,5-dimethyloctane, 1.8-diamino-2,2-dimethyloctane,1.8-diamino-3,3-dimethyloctane, 1,8-diamino-4,4-dimethyloctane,1,6-diamino-2,4-diethylhexane, 1,9-diamino-5-methylnonane,1,11-diaminoundecane, and 1,12-diaminododecane.

Exemplary recurring units (R_(PA)) of the polyamide are notably:

-   (i) —NH—(CH₂)₅—CO—, i.e. recurring units which can be notably    obtained via polycondensation reaction of ε-caprolactam;-   (ii) —NH—(CH₂)₈—CO—, i.e. recurring units which can be notably    obtained via polycondensation reaction of 9-aminononanoic acid;-   (iii) —NH—(CH₂)₉—CO—, i.e. recurring units which can be notably    obtained via polycondensation reaction of 10-aminodecanoic acid;-   (iv) —NH—(CH₂)₁₀—CO—, i.e. recurring units which can be notably    obtained via polycondensation reaction of 11-aminoundecanoic acid;-   (v) —NH—(CH₂)₁₁—CO—, i.e. recurring units which can be notably    obtained via polycondensation reaction of laurolactam;-   (vi) —NH—(CH₂)₆—NH—CO—(CH₂)₄—CO—, i.e. recurring units which can be    notably obtained via polycondensation reaction of hexamethylene    diamine and adipic acid;-   (vii) —NH—(CH₂)₆—NH—CO—(CH₂)₈—CO—, i.e. recurring units which can be    notably obtained via polycondensation reaction of hexamethylene    diamine and sebacic acid;-   (viii) —NH—(CH₂)₆—NH—CO—(CH₂)₁₀—CO—, i.e. recurring units which can    be notably obtained via polycondensation reaction of hexamethylene    diamine and dodecanoic acid;-   (ix) —NH—(CH₂)₁₀—NH—CO—(CH₂)₁₀—CO—, i.e. recurring units which can    be notably obtained via polycondensation reaction of decamethylene    diamine and dodecanoic acid;-   (x) —NH—(CH₂)₆—NH—CO—(CH₂)₇—CO—, i.e. recurring units which can be    notably obtained via polycondensation reaction of hexamethylene    diamine and azelaic acid (otherwise known as nonandioic acid);-   (xi) —NH—(CH₂)₁₂—NH—CO—(CH₂)₁₀—CO—, i.e. recurring units which can    be notably obtained via polycondensation reaction of dodecamethylene    diamine and dodecanoic acid;-   (xii) —NH—(CH₂)₁₀—NH—CO—(CH₂)₈—CO—, i.e. recurring units which can    be notably obtained via polycondensation reaction of decamethylene    diamine and decanoic acid;-   (k) —NH—(CH₂)₄—NH—CO—(CH₂)₄—CO—, i.e. recurring units which can be    notably obtained via polycondensation reaction of 1,4-butanediamine    and adipic acid; and-   (kk) —NH—(CH₂)₄—NH—CO—(CH₂)₈—CO—, i.e. recurring units which can be    notably obtained via polycondensation reaction of 1,4-butanediamine    and sebacic acid.

Preferably, the polyamide consists essentially of recurring units(R_(PA)), as above detailed, being understood that end-chain, defectsand other irregularities can be present in the polyamide chain, withoutaffecting the properties thereof.

Recurring units (R_(PA)) of the polyamide can be all of the same type,or can be of more than one type, that is to say that the polyamide (PA)can be a homo-polyamide or a co-polyamide.

Specific examples of the polyamides which can be advantageously used inthe hereby provided composition are notably:

-   -   polyamide 6; polyamide 6,6 and mixtures and co-polyamides        thereof.

Particularly preferred polyamide to be used in the composition of thepresent invention is polyamide 6,6.

In the present invention, an amount of at least one polyamide is from21.0 wt % to 99.6 wt % with respect to the total weight of thecomposition. Preferably, the amount of at least one polyamide is from30.0 wt % to 99.1 wt %, more preferably 40.0 wt % to 98.7 wt % withrespect to the total weight of the composition.

The polyamide a) of the present invention comprises carboxylic acidgroups; these groups may be present at the terminal end of the polyamideand/or distributed along the polyamide chain. These carboxylic acidgroups are capable of reacting with the isocyanate groups of thecompound c) according the following reaction:

In general, the foamable composition of the present invention comprisesa respective amount of carboxylic acid groups and of isocyanate groupsthat is adapted to the desired release of gas, especially CO₂, and thusto the density of the foam obtained from the foamable composition.

In the present invention, the term “thermoplastic rubber” is intended todenote, in particular, a compound imparting flexibility to a polyamidea) of the present invention.

Examples of the thermoplastic rubber in the present invention comprise,but are not limited to, polyolefins, polystyrenes, polyesters,acrylonitrile-butadiene-styrene (ABS) copolymers, polyvinyl chloride(PVC), unplasticized polyvinyl chloride (UPVC), acrylic polymers, andthe like.

In one embodiment of the present invention, the thermoplastic rubbercomprises ethylene propylene diene rubber (EPDM), ethylene propylenerubber (EPM), and the like.

The term “styrenic thermoplastic elastomer (STPE)” of the presentinvention is intended to denote, in particular, a styrene-basedthermoplastic elastomer and mention may be made ofstyrene-ethylene/butylene-styrene (SEBS),styrene-ethylene/propylene-styrene (SEPS),styrene-ethylene/ethylene/propylene-styrene (SEEPS), and anycombinations thereof.

In the present invention, an amount of at least one thermoplastic rubberis from 0.3 wt % to 9.0 wt % with respect to the total weight of thecomposition. Preferably, the amount of at least one thermoplastic rubberis from 0.7 wt % to 6.0 wt %, more preferably 1.0 wt % to 4.5 wt % withrespect to the total weight of the composition.

In the present invention, the compound having at least one isocyanategroup preferably is a polyisocyanate, that is to say a compoundcomprising at least two isocyanate groups.

The polyisocyanate of the invention is preferably a polyisocyanate offormula (I) below:Y—(—N═C═O)_(n)  (I)

in which Y is a substituted or unsubstituted aromatic, aliphatic,cycloaliphatic or heterocyclic multivalent group optionally comprisinghetero atoms and n is at least equal to 2. Examples of polyisocyanatesthat may be suitable are isophorone diisocyanate, 1,3- and1,4-cyclohexane diisocyanate, 1,2-ethylene diisocyanate,1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,2,4-and 2,4,4-trimethyl-1,6-hexamethylene diisocyanate, 1,12-dodecanediisocyanate, α,α′-diisocyanatodipropyl ether, 1,3-cyclobutanediisocyanate, 2,2- and 2,6-diisocyanato-1-methylcyclohexane, 2,5- and3,5-bis(isocyanatomethyl)-8-methyl-1,4-methanodecahydronaphthalene,1,5-, 2,5-, 1,6- and2,6-bis(isocyanatomethyl)-4,7-methanohexahydroindane, 1,5-, 2,5- and2,6-bis(isocyanato)-4,7-methanohexahydroindane, 2,4′- and4,4′-dicyclohexyl diisocyanate, 2,4- and 2,6-hexahydrotolylenediisocyanate, perhydro-2,4′- and 4,4′-diphenylmethane diisocyanate,α,α′-diisocyanato-1,4-diethylbenzene, 1,3- and 1,4-phenylenediisocyanate, 4,4′-diisocyanatobiphenyl,4,4′-diisocyanato-3,3′-dichlorobiphenyl,4,4′-diisocyanato-3,3′-dimethoxybiphenyl,4,4′-diisocyanato-3,3′-dimethylbiphenyl,4,4′-diisocyanato-3,3′-diphenylbiphenyl, 2,4′- and4,4′-diisocyanatodiphenylmethane, 1,5-naphthylene diisocyanate, 2,4- and2,6-tolylene diisocyanate,N,N′-(4,4′-dimethyl-3,3′-diisocyanatodiphenyl)uretdione, m-xylylenediisocyanate, dicyclohexylmethane diisocyanate, tetramethylxylylenediisocyanate, 2,4,4′-triisocyanatodiphenyl ether,4,4′,4′-triisocyanatotriphenylmethane, and analogues and mixturesthereof.

In the present invention, polyisocyanates, such as a diisocyanate, i.e.a polyisocyanate comprising two isocyanate groups, or a triisocyanate,i.e. a polyisocyanate comprising three isocyanate groups, areparticularly advantageous.

According to a first embodiment, the polyisocyanate can be monomericpolyisocyanate as listed above.

According to a second embodiment, the polyisocyanate can be oligomericpolyisocyanate. Examples of such oligomeric polyisocyanate that may bementioned include hexamethylene diisocyanate trimers (HDI trimers orHDT) such as Tolonate HDT® and biurets such as Tolonate HDB®. Otherexamples of oligomeric polyisocyanates are aliphatic oligomericisocyanates, such as isophorone diisocyanate dimers or trimers, and alsohexamethylene diisocyanate derivatives of high functionality and lowviscosity, and norbornene diisocyanate dimers and trimers. Examples ofpolyisocyanate mixtures that may be mentioned include isocyanate trimerssuch as HDT and isophorone diisocyanate trimer (IPDT). Polyisocyanatesof tolylene diisocyanate (TDI) or of methanediphenyl isocyanate (MDI)derivatives may also be used.

In the present invention, the amount of at least one compound having atleast one isocyanate group is from 0.1 wt % to 3.0 wt % with respect tothe total weight of the composition. Preferably, the amount of at leastone compound having at least one isocyanate group is from 0.2 wt % to2.0 wt %, more preferably 0.3 wt % to 1.5 wt % with respect to the totalweight of the composition.

In the present invention, a ratio of the at least one thermoplasticrubber to the at least one compound having at least one isocyanate groupis from 2:1 to 4:1, preferably around about 3:1.

The composition according to the present invention may optionallycomprise d) at least one filler.

In the present invention, the term “filler” is intended to denote, inparticular, a material added to a polymer composition to improve itsproperties and/or to reduce the cost. Such materials can be in the formof solid, liquid or gas. By appropriately selecting these materials, notonly the economics but also other properties such as processing andmechanical behavior can be improved. Although these fillers retain theirinherent characteristics, very significant differences are often seendepending on the molecular weight, compounding technique and thepresence of other additives in the formulation. Therefore, once thebasic property requirements are established, the optimum type and theloading level of the filler for the balance between cost and performancemust be determined.

In the present invention, the filler is preferably selected from thegroup consisting of glass fibres, glass beads, calcium carbonate,silicates, talc, kaolin, mica, carbon black, graphite, wood powders, andpowders and fibres of other natural products, and synthetic fibres.Glass fibres are most advantageously used in the composition of thepresent invention.

In the present invention, an amount of at least one filler may be from 0to 65.0 wt %, preferably from 0 wt % to 50.0 wt %, more preferably from0 wt % to 45.0 wt % with respect to the total weight of the composition.When filler is present in the composition, its amount will be generallycomprised between 5.0 and 65.0 wt %, preferably between 10.0 and 50.0 wt%, more preferably between 15.0 and 45.0 wt % with respect to the totalweight of the composition.

In addition, the composition according to the present invention mayoptionally comprise d) at least one additive. Examples of the additives,which may be advantageously used, include an antioxidant, a pore-formingagent, a surfactant, a nucleating agent, a plasticizer, a matting agent,a pigment, a colorant, a heat stabilizer, a light stabilizer, abioactive agent, an antisoiling agent, an antistatic agent, a flameretardant, and a catalyst to accelerate the decarboxylation by reactionof the carboxylic acid functional group with the isocyanate functionalgroup. The examples of the catalyst comprise, but are not limited to,tertiary amines, such as diazabicyclooctane (DABCO),diazabicycloundecene (DBU), triethylamine (TEA), and the like.

In the present invention, an amount of at least one additive may be from0 to 2.0 wt %, preferably 0 to 1.5 wt %, more preferably 0 to 1.0 wt %with respect to the total weight of the composition. The range ofconcentration by weight of the additive, if contained in the compositionof the present invention, may be from 0.1 to 2.0 wt %, preferably from0.5 to 1.0 wt % with respect to the total weight of the composition.

Another aspect of the present invention is to provide a method forproducing the composition according to the present invention.

The method comprises i) preparing a master-batch comprising a mixture ofb) at least one thermoplastic rubber and c) at least one compound havingat least one isocyanate group; heating a) at least one polyamidecomprising at least one carboxylic group and optionally d) at least onefiller and e) at least one additive at a temperature equal to or greaterthan a melting point of the polyamide to obtain a molten polyamidematrix; and iii) adding at least a portion of the master-batch to themolten polyamide matrix. Thusly-obtained product can be furtherstabilized. The stabilization can be accomplished physically (forexample, by cooling to a temperature below the melting point of thepolyamide) and/or chemically (for example, by crosslinking thepolyamide). Cooling is generally obtained by carrying out a quenching,which results in a rapid decrease of the temperature. The crosslinkingof the polyamide can be carried out by addition of crosslinking agentsknown to a person skilled in the art. In general, these are compoundscomprising at least two functional groups which react with the acidand/or amine functional groups of the polyamide. Mention may be made, asexamples of crosslinking agents, of carbonylbislactams, such ascarbonylbiscaprolactam, bisoxazine, bisoxazoline, and the like. Thestabilization is advantageously carried out physically and by cooling.

In this regard, it is difficult to introduce a compound having at leastone isocyanate group to a molten polyamide, because said compound isoften deteriorated when being introduced into a molten polyamide matrix,and thus, only a partial portion of isocyanate groups in the compoundare introduced into the molten polyamide, which results in lessgeneration of CO₂ than expected.

In order to overcome said disadvantage, a master-batch comprising amixture of b) at least one thermoplastic rubber and c) at least onecompound having at least one isocyanate is thus prepared prior to beingadded to a) at least one polyamide comprising at least one carboxylicgroup which is in a molten state through the heating step ii) of themethod of the present invention.

The method of the present invention comprises adding a pre-preparedmixture of a thermoplastic rubber and a compound having at least oneisocyanate group to a molten polyamide, and in this manner, enablesintroducing relatively large portion, preferably a full amount ofisocyanate groups of the compound c) into the polyamide matrix.

The temperature to be achieved during the heating step ii) is greaterthan or equal to the melting point of the polyamide of the composition.Advantageously, this temperature is greater than or equal to T(° C.)+10,preferably greater than or equal to T(° C.)+15, T(° C.) being themelting point of polyamide of the composition.

Fillers d) as above detailed as well as additives e) as above listed canbe introduced during the heating step ii) or in any step conductedlater-on.

The preparation of a foamable polyamide composition of the invention andthe preparation of a polyamide foam therefrom can be carried out eitherseparately or simultaneously. In case they are carried outsimultaneously, both processes can be carried out in an identicaldevice, such as an extrusion device. The extrudate from the device maybe subsequently cooled and solidified as it is pulled through the die,which results in a desired shape of the polyamide foam.

The composition according to the present invention is foamable.Therefore, the present invention also pertains to a foam obtained fromthe composition of the present invention.

In order to obtain a foam in a desired shape from the composition of thepresent invention, a molding device, injection molding device, thermalforming or compressing device, for example of Sheet Molding Compound(SMC) type, injecting/blow molding device, extrusion device,extrusion/blow molding device, and the like may be employed depending onthe requirements.

Further aspect of the present invention relates to a use of the foam asa light-weight material in aeronautical or motor vehicle, packaging orsound insulation applications, preferably in motor vehicle applications,such as bumpers, seating, dashboard, fuel systems, vehicle bodyincluding panels, under-bonnet components, interior trim, electricalcomponents, exterior trim, lighting, upholstery, liquid reservoirs,etc., and to a motor vehicle comprising the foam according to thepresent invention. The weight of the motor vehicle may be reduced byincorporating the foam as a light-weight material into a motor vehicle,which accordingly results in the reduction of the energy consumption andalso potential reduction of carbon dioxide emissions to theenvironments.

Other details or advantages of the present invention will become moreclearly apparent through the examples given below. The present inventionwill be elucidated by the following examples, which are intended todemonstrate, but not to restrict, the invention.

EXAMPLES

The compositions used are as follows:

Examples 1 and 2 (for Comparative Examples): mixtures of polyamide 6,6,HDB (hexamethylene diisocyanate biuret), glass fiber and antioxidant.

Examples 3 and 4: mixtures of polyamide 6,6, HDB, SEBS(styrene-ethylene/butylene-styrene), glass fiber and antioxidant.

Chemical reagents used in the Examples are specified as follows:

-   -   HDB: Tolonate HDB® from VencoreX    -   SEBS: Taipol® 6150 from Third Sector Research Centre (TSRC)    -   Glass fiber: 289H from Nippon Electric Glass (NEG)    -   Polyamide: Technyl® 27B10 from Solvay    -   Antioxidant: Irganox® B1171 from BASF

The compositions prepared are detailed in Table 1 below. The proportionsare indicated in weight percentages in the composition.

TABLE 1 Ex. 1 Comp. Ex. 2 Comp. Ex. 3 Ex. 4 Polyamide 69.1 68.8 67.766.7 HDB 0.6 0.9 0.6 0.9 SEBS 0 0 1.4 2.1 Glass fiber 30 30 30 30Antioxidant 0.3 0.3 0.3 0.3 Total 100 100 100 100

Comparative Examples 1 and 2 (Hereinafter, Ex, 1 and 2 Comp.)

Heating polyamide 6,6 was carried out at a temperature of greater thanor equal to its melting point to produce a molten polyamide 6,6. Ex. 1and 2 Comp. were obtained by mixing said molten polyamide 6,6, HDB,glass fiber, and antioxidant together in a TES-30 twin-screwco-extrusion type extruder from JSW (Japan Steel Works) Corporation,with a screw length/diameter ratio of 40, while glass fibers beingintroduced through side feeder. The extrusion temperatures were250-250-250-250-260-260-230-210-150° C. from nozzle to hopper, and thethroughput and RPM were 30 kg/hr and 300, respectively.

The extrudates were then cooled in water at room temperature. Thefoaming ratio was determined as 2.8% and 4.2%, respectively, withrespect to the total volume of Ex. 1 and 2 Comp.

Further, the flexural strength and the flexural modulus were measuredusing a Universal Test Machine (UTM) according to ASTM D790. Inaddition, the notch Izod was measured according to ASTM D256.

Examples 3 and 4 (Hereinafter, Ex. 3 and 4)

The master-batches for Ex. 3 and 4 were first prepared by mixing SEBSand HDB together. A molten polyamide 6,6 matrix was likewise produced byheating polyamide 6,6, glass fibers and antioxidant together at atemperature of greater than or equal to the melting point of polyamide6,6. Said master-batches were subsequently introduced into the moltenpolyamide 6,6 matrix through a side feeder to obtain Ex. 3 and 4,respectively.

Ex. 3 and 4 were placed in the same extruder. The extrusion conditionswere the same with those for Ex. 1 and 2 Comp.

The extrudates were likewise cooled in water at room temperature. Thefoaming ratio was determined as 11.6% and 14.8%, respectively, withrespect to the total volume of Ex. 3 and 4.

Flexural strength, flexural modulus, and notch Izod were also measured.The measurement was performed using the same conditions and the sameinstrument, as detailed above.

The foaming ratio and the above mechanical parameters of the foamobtained from the Examples 1 to 4, which correspond to Ex. 1 and 2 Comp.and Ex. 3 and 4, respectively, are summarized in Table 2 below.

TABLE 2 Ex. 1 Comp Ex. 2 Comp Ex. 3 Ex. 4 Foaming Ratio (%) 2.8 4.2 11.614.8 Flexural strength (MPa) 244 238 231 221 Flexural modulus (MPa)8,200 8,000 7,500 7,100 notch Izod (J/m) 135 130 125 110

As being confirmed from the experimental data in Table 2, the foamingratios of Ex. 3 and 4 were noticeably increased compared to those of Ex.1 and 2 Comp. Also, mechanical properties of the Examples 3 and 4,including flexural strength, flexural modulus and notch Izod, were stillin a satisfactory level to be used as a light-weight material in a motorvehicle application such as engine cover, rocker box, etc.

The invention claimed is:
 1. A foamable composition consistingessentially of: a) 21.0 to 99.6 wt % of a polyamide 6,6 comprising atleast one carboxylic group; b) 1.0 to 4.5 wt % of astyrene-ethylene/butylene-styrene thermoplastic elastomer; c) 0.1 to 3.0wt % of hexamethylene diisocyanate biuret; d) 0 to 65.0 wt % of at leastone filler selected from the group consisting of glass fibers, glassbeads, calcium carbonate, silicates, talc, kaolin, mica, carbon black,graphite, wood powders, and synthetic fibers; and e) 0 to 2.0 wt % of atleast one additive; wherein the sum of wt % of the components a) to e)is 100 wt % of the composition.
 2. The foamable composition according toclaim 1, wherein the at least one additive is selected from the groupconsisting of an antioxidant, a pore-forming agent, a surfactant, anucleating agent, a plasticizer, a matting agent, a pigment, a colorant,a heat stabilizer, a light stabilizer, a bioactive agent, an antisoilingagent, an antistatic agent, flame retardant, and a catalyst toaccelerate decarboxylation by reaction of the carboxylic acid functionalgroups with isocyanate functional groups.
 3. The foamable compositionaccording to claim 1, wherein the composition includes about 5 to 65.0wt % of the at least one filler.
 4. The foamable composition accordingto claim 1, wherein the at least one filler is selected from the groupconsisting of glass fibers, glass beads, calcium carbonate, silicates,talc, kaolin, mica, carbon black, graphite, and wood powders.
 5. Thefoamable composition according to claim 1, wherein the at least onefiller is glass fibers.
 6. The foamable composition according to claim1, wherein the composition consists essentially of: a) 40.0 to 98.7 wt %of the polyamide 6,6 comprising at least one carboxylic group; b) 1.0 to4.5 wt % of the styrene-ethylene/butylene-styrene thermoplasticelastomer; c) 0.3 to 1.5 wt % of the hexamethylene diisocyanate biuret;d) 15 to 45.0 wt % of the at least one filler selected from the groupconsisting of glass fibers, glass beads, calcium carbonate, silicates,talc, kaolin, mica, carbon black, graphite, wood powders, and syntheticfibers; and e) 0.1 to 2.0 wt % of the at least one additive.
 7. A methodfor producing the foamable composition according to claim 1, comprising:i) preparing a master-batch comprising a mixture of thestyrene-ethylene/butylene-styrene thermoplastic elastomer and thehexamethylene diisocyanate biuret; ii) heating the polyamide 6,6; andoptionally the at least one filler at a temperature equal to or greaterthan a melting point of the polyamide to obtain a molten polyamidematrix; and iii) adding at least a portion of the master-batch to themolten polyamide matrix.
 8. A foam obtained from the foamablecomposition according to claim
 1. 9. An aeronautical vehicle, a motorvehicle, packaging, or sound insulation comprising the foam according toclaim
 8. 10. A motor vehicle comprising the foam according to claim 8.